[
    "12.345.67.89"
]

cat publicIpAddress.log | sed 's/[][]//g'

"12.345.67.89"

ipd=$( cat publicIpAddress.log | sed 's/[][]//g' )

ipd=$( cat publicIpAddress.log | sed 's/[][]//g' ) | xargs

ipd=$( cat publicIpAddress.log | sed 's/[][]//g' ) | tr -d '"'

ipd=$( cat publicIpAddress.log | sed 's/[][]//g' )
ipd=$( "${ipd//"}" )

ipd=$( cat publicIpAddress.log | sed 's/[][]//g' ) | sed -e 's/^"//' -e 's/"$//'